1. Technical Field of the Invention
The present invention relates in general to communication systems, and in particular, to wavelength division multiplexing (WDM) fiber-optic communication systems.
2. Description of Related Art
In fiber-optic communication systems, wavelength-division multiplexing (WDM) is commonly used to multiplex multiple optical carrier signals (channels) onto a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. Traditionally, the only optical interfaces available on equipment connected to the client side of WDM transmission equipment were not wavelength-controlled and were only suitable for short reach transmission. However, router vendors are increasingly adding dense WDM (DWDM) long reach interfaces as options on their products. The availability of these client side DWDM interfaces has led to a demand for “alien wavelength” transport over WDM transmission equipment, i.e. the direct connection of the third party DWDM optical signal to the transmission equipment optical multiplexer.
The optimum line operating conditions and relative channel powers need to be determined on systems carrying these alien wavelengths. On WDM long haul systems employing transponders from only one vendor, the optimum signal levels through the line together with the optimum channel powers could be determined by accessing the pre FEC error counters at the far end transponders. However, when transporting alien wavelengths, the WDM signals may be generated and received by equipment supplied by other manufacturers, and it is generally not practical to access the third party equipment pre FEC error counters.
Transmitting all channels at the same power is an adequate solution in metro/regional systems when all the channels have similar transmission characteristics. However, there is increasingly a need to support OC-48, OC-192, OC-768 and 100 GbE simultaneously within one system. A variety of modulation formats exist for transporting these signals, each with there own transmission requirements. Therefore, a need exists for automatically optimizing a line and adjusting the relative channel powers to obtain the best possible performance in a system carrying different traffic types originating from a multitude of different manufacturers equipment.